The present invention relates to an aircraft provided on either side of its fuselage with at least one lift structure constituted by at least two wings whose distal ends are connected either to each other or to at least one wing element, each structure forming in front elevation with the sides of said fuselage a closed polygon, and comprising an upper wing and a lower wing, the zone of attachment of the latter on the fuselage possibly being offset in the direction of streamline flow with respect to the zone of attachment of the upper wing.
It is known that an aircraft wing must present a profile and characteristics which are determined as a function of contradictory imperatives. In fact, it is necessary, among other obligations, to delay the phenomenon of laminar separation, to reduce, or even eliminate, the marginal leaks, and finally to reduce the flow disturbances at the connection of the wing on the one hand to the fuselage and on the other hand to the mobile parts. Now, for a wing profile complying with the first condition mentioned above, the wing aspect ratio makes it possible to solve the difficulties associated with the two conditions mentioned. Nevertheless, this ratio can only be limited, having regard to the dimensions of the aircraft. One solution lies in the fold of the wing on itself, and therefore in the production of structures with superposed multiple wings.
Aircraft provided with such lifting structures incorporating multiple wings are already known.
However, such known aircraft present drawbacks. In fact, the difficulties associated with the lack of rigidity of such structures are solved only by increasing the sections, particularly at the roots, due to the presence of a bending moment appearing at that spot. This increase in the thickness of the wing presents consequences which are detrimental to the weight of such wing elements.